All radio units have a receiver and/or transmitter circuitry and an antenna. The antenna is needed for conversion between radio signals and electric radio frequency signals. It is known that the antenna should be sensitive in the frequency range or ranges in which the antenna is designed to operate. There are various different antenna designs in which a local or global resonance maximum appears at desired sensitive frequency ranges.
Radio units may be used in various different applications. In some cases, the radio unit may be particularly designed as an entity so that all the circuitry in the immediate proximity of the antenna is designed to enable faultless operation of the antenna. For example, a television or radar antenna is typically spaced far apart from other objects. In some applications, a generic radio unit is squeezed into portable device. The antenna may be surrounded with circuitries that alter the operation of the antenna. For instance, there may be numerous different antennas in a cellular phone for wireless local area network, for Bluetooth, for near field communications and for different cellular and satellite communications. Hence, each radio unit may require particular customization to ensure desired operation in its operation environment. For instance, the antenna placement, antenna characteristics and/or matching of the antenna may be varied on production line for each portable radio device. Moreover, the radio units may also have some variance even if built with common specification so that in some cases, cascading tuning operations may be needed to ensure desired operation of portable radio devices.